Introduction: Inflammatory bowel disease leads to chronic inflammation of all or part of the digestive tract and damage to the intestinal lining. Current treatment plans focus on systemic or intestinal delivery of drugs to either suppress the immune system or interrupt inflammatory pathways; however these drugs frequently fail or are inadequate to prevent or reverse the damage [1],[2]. The goal of this research is to develop a new class of treatment options that specifically target the diseased area and locally deliver stem cells and drugs through sprayable formation of a regenerative hydrogel that can be applied during diagnostic procedures in order to prevent the need for bowel resection and provide a higher quality of life for patients. The objective of this study was to evaluate the sprayable administration of cellular thermoresponsive hydrogel solutions, which can solidify immediately on contact with warm body tissue and create a homogeneous therapeutic coating on the diseased tissue. The effects of spraying parameters, spraying technique, and hydrogel composition were investigated in vitro, and the efficacy of rapid and minimally-invasive application of cellular coatings to the intestinal wall was demonstrated ex vivo.
Materials and Methods: Poly(N-isopropylacrylamide) was copolymerized with glycidyl methacrylate to form thermogelling macromers (TGMs), and polyamidoamine (PAMAM) crosslinkers were created from piperazine and methylene bisacrylamide [3]. TGM and PAMAM macromers were dissolved separately in PBS or cell culture media. Upon macromer mixing and spraying the solution onto a surface (either glass, tissue culture plastic or porcine intestines) at 37°C, the solutions immediately solidified due to the thermogelation mechanism. In addition, cellular hydrogels were created by mixing suspended cells into the solution just prior to spraying. The effects of spray pressure, polymer composition, and spraying technique (single-stream, layer-by-layer and dual-stream spraying) on hydrogel properties and cell viability were investigated. Swelling and viscoelastic properties of the hydrogels were determined by gravimetric and rheological methods, respectively. Cell compatibility was determined by Live/Dead analysis.
Results and Discussion: Uniform, thick hydrogels coatings were obtained by spraying solutions under 1 bar of pressure, and hydrogel hydrophilicity and thickness were controlled by the concentration of PAMAM crosslinker (Figure 1). Moreover, decreased viscosity, pressure, and crosslinking led to enhanced cell viability in the hydrogel. Compared to layer-by-layer and single-stream spraying, dual-stream hydrogels demonstrated maximum cell viability (Figure 2).
Figure 1. Weight swelling ratios of hydrogels depending on the content of PAMAM. Inset figure: sprayed hydrogels.
Figure 2. Fluorescent microscopy images of (A) sprayed cells in media; encapsulated cells in single-stream-sprayed 10 wt. % TGM hydrogels with 0, 6, and 10 wt. % PAMAM (B, C, and D, respectively); and cells encapsulated in 10 wt.% TGM and 10 wt.% PAMAM hydrogels sprayed with either a layer-by-layer (E) or simultaneous dual-stream (F) method.
Conclusion: Sprayable, in situ forming hydrogels capable of delivering populations of cells and creating a homogeneous therapeutic coating on diseased bowel tissue were demonstrated and offer promise as novel therapies for applications in regenerative medicine.
Prof. Abigail N. Koppes; Adedokun Adedoyin; Robert Eagan
References:
[1] P.L. Lakatos, Recent trends in the epidemiology of inflammatory bowel diseases: up or down? World Journal of Gastroenterology 12 (2006) 6102
[2] S.B. Hanauer, Inflammatory bowel disease: epidemiology, pathogenesis, and therapeutic opportunities, Inflamm. Bowel Dis. 12 (2006) S3-S9
[3] A.K. Ekenseair, K.W. Boere, S.N. Tzouanas, T.N. Vo, F.K. Kasper, A.G. Mikos, Synthesis and characterization of thermally and chemically gelling injectable hydrogels for tissue engineering, Biomacromolecules 13 (2012) 1908-1915.